An automatic control system for friction-encumbered signaling-devices is disclosed by the German Published Patent Application 32 07 863 (which is a German counterpart to U.S. Pat. No. 4,499,412). The application also describes a regulating device for a friction-encumbered signaling-device. According to the application, the load side of a two-step action controller is connected to a non-linear automatic controller. This two-step action controller only switches from one step to the other when the difference between the setpoint value and the actual value of the closed-loop control circuit changes. At the balance point, the non-linear automatic controller shows a steep, yet normally flat characteristic curve. A limiting device suppresses the switching rates when they are too high. This prevents the two-step action controller from switching back and forth at a too frequent rate. The described system has an analog design.
The German Published Patent Application 32 33 290 (which is a German counterpart of U.S. Pat. No. 4,594,993) describes a device for automatically controlling the feedback rate of exhaust gas from a diesel engine. A linear automatic controller supplies the input variable to a three-step controller. According to the operation of the device, the three-step controller only switches when the difference between the setpoint value and the actual value of the closed-loop control circuit changes. Hysteresis prevents the three-step controller from constantly switching back and forth.
The German Published Patent Application 27 26 987 discloses splitting a regulating device into a digital and an analog component. The digital component processes the digital data, and the analog component processes the analog data.